1. Field of the Invention
The present invention relates to a display panel control device, a liquid crystal display device, an electric appliance, a display device driving method, and a control program.
2. Description of the Related Art
A hold-type display device holds an image as a still image within a frame period, and displays a dynamic image by switching a screen for every frame. With dynamic image displays provided on the hold-type display device, still images are switched and displayed continuously without a break from frame to frame. Thus, human beings whose eyesight moves by following the dynamic image display perceive still images held still as images that are superimposed on one another in a shifted manner, and recognize that state as dynamic image blur.
In a liquid crystal display device as an example of such hold-type display device, there has been proposed black insertion drive which drives the device by inserting black display to video display of a frame period, in order to improve the dynamic image blur.
With the black insertion drive for the liquid crystal display device, a black display signal is written to pixels of a liquid crystal display panel after a video signal is written thereto, by providing a video display period and a black display period within one frame. Therefore, it is necessary to increase a panel writing frequency, so that the hold time of the liquid crystal is shortened.
Therefore, as depicted in Japanese Unexamined Patent Publication 2004-253827 (Patent Document 1), for example, there has been proposed a technique to increase the response speed by performing overshoot drive in the black insertion drive with which black display and video display are repeated alternately by each sub-frame.
In the liquid crystal display device of Patent Document 1, a black display signal is inserted by a black inserting device after converting a video signal to “N×”-speed by a frame frequency converting device. Thereafter, information necessary for emphasis conversion (overshoot) is obtained by an emphasis converting device from an OS (overshoot) table memory so as to perform emphasis conversion processing on the video signal.
With this emphasis conversion processing, when writing a black display signal after writing of a video signal, the emphasis conversion processing (overshoot drive) is applied on the video signal by using an emphasis conversion parameter that is set by considering gradation luminance (of the black display) to which the liquid crystal can actually reach within a black display period (paragraph number 0074). Even if the liquid crystal does not completely respond and reach a black gradation (0-gradation) within the black display period, it is possible to perform the emphasis conversion processing to display image data in a following video display period based on the actual finally-reached gradation (0-gradation).
That is, with the technique depicted in Patent Document 1, the emphasis conversion processing (overshoot) is performed based on a single OS table memory and, even if the gradation value of the black signal is unreached during one frame period, the amount of overshoot applied to the video signal is downwardly-adjusted from 118-gradation (that is original amount to be applied) to 70-gradation (FIG. 14 and FIG. 18 of Patent Document 1) so as to prevent whitening of the pixels.
However, even when normal overshoot (emphasis adjustment) is applied on the video signal in the black insertion drive with the liquid crystal display device of Patent Document 1, there is delay caused in response of the liquid crystal if there is a difference generated in the gradation voltage values (gradation voltages) of the video signals between a given frame and another frame. Because of this, it is not possible to reach a prescribed luminance within a video display period of another frame. As a result, as shown in FIG. 47, there are points that need to be improved in the video display, such as generation of step-like tailing, etc., and ghost generated in scroll-display of letters, which causes bad influences on the image quality.
Particularly, the technique of Patent Document 1 takes no consideration over the unreached response of the gradation value of the video signal, other than applying the conversion adjustment by normal overshoot. Thus, when the gradation value of the video signal is increased in a next frame, it is not possible to reach the prescribed luminance (transmittance), thereby generating the tailing and ghost.
Further, with the technique of Patent Document 1, the overshoot amount of a prescribed gradation is reduced to equalize each gradation voltage for each frame. However, unreached response to be in the black display (insufficient blackening of black display) is not improved, and the luminance (transmittance) does not completely respond to reach the black gradation (0-gradation) within the black display period (sub-frame period) (FIG. 14, FIG. 18, etc., of Patent Document 1). Therefore, the step-like tailing is also generated in the video display with this technique.
Particularly, when there is a difference generated in the gradation values (gradation voltages) in the video display of each frame, not only unreached response of the black display but also there is a difference generated in the luminance (blackening of the black display) of the black display in each frame, as shown in FIG. 47. This results in having ghost at the time of video display, which is a point that needs to be improved. In addition, the difference in the blackening states of the black displays gives influences accumulatively in the following frames, and the luminance of the video display changes accumulatively in accordance with the influences. This is a cause for generating the tailing, and the ghost in the scroll display of letters.
Further, even if the luminance of each video display in each frame is made almost uniform, the ghost-like tailing cannot be improved.